This invention relates to a floppy disk unit which is capable of using, by the same unit, various kinds of disk mediums that are used by the units with different speed of rotation of the spindles.
The conventional speeds of rotation of the spindle of the conventional 51/4" floppy disk unit and 8" floppy disk unit are 300 rpm respectively, and 360 rpm, but recent technical progress has made it possible to bring the speed of rotation of the spindle of a 51/4" floppy disk unit to 360 rpm, and thereby the 51/4" floppy disk unit is now used with the same specifications as that of the 8" floppy disk unit. In this case, the disk mediums which have been used by the conventional 51/4" floppy disk unit of 300 rpm can no longer be used by the 51/4" floppy disk unit of 360 rpm and thereby implantation of software cannot be realized easily.
For example, a disk medium 1 may have a data transfer speed of 4 .mu.s/bit at a speed of rotation of 300 rpm, while a disk medium 2 has a data transfer speed of 2 .mu.s/bit at a speed of rotation of 360 rpm. Usually, each of the disk medium 1 and the disk medium 2 can be read or written only with a respective exclusive drive unit. On the other hand, a floppy disk controller side can cope with any disk medium, in case the disk mediums 1, 2 are used in the respective exclusive drive units, simply by dividing the fundamental clock frequency for reading and writing by into 1/2, because the data transfer speed is simply given as the ratio of 1:2.
However, in case the disk medium 1 is used with the exclusive driver for the disk medium 2, the data transfer speed becomes 3.33 .mu.s/bit and therefore division of the fundamental clock frequency of the floppy disk controller alone cannot make it possible to read and write the data.